In certain installations, such as in audio frequency (AF) track circuit equipment for railroad and mass and/or rapid transit operations, it is mandatory to ensure the safety and security of the crewmen and/or passengers as well as to protect the system and apparatus against damage and/or destruction by a false or unsafe condition. Thus, it is essential to exercise extreme care in designing the circuitry and selecting the components of the electronic track circuit equipment to ensure fail-safe operation. In the past, it had been found that the code rate representing the speed commands could be inadvertently increased when frequency of the output signals of the nonvital oscillating circuit decreased due to a component or circuit failure. For example, during documentation of the fail-safe testing, the speed command code rate of the code rate generator was unsafely increased from 180 Hz to 270 Hz when the output frequency of the previously designed voltage supply oscillator decreased from 6K Hz to 875 Hz.